The present invention relates to a cable made of twisted wire pairs, and more particularly, to a cable made of twisted wire pairs that is suitable for use in high-speed data communication applications.
Twisted pair telecommunication wires are bundled together in large cables. Typically, 50 or more pairs of wire are included in a typical cable configuration near its termination point. However, cables coming out of a central telecommunications location may have hundreds or even thousands of pairs bundled together. In operation, each twisted pair within the cable is utilized for transmitting data as well as for furnishing direct current (DC) power to remote equipment. With signal multiplexing, a single twisted pair may service multiple data signals and multiple end users, reducing the number of individual pairs required for a desired level of service and reducing the distance between an access point and a final subscriber.
Recently, demands upon telecommunication systems have greatly increased. With the explosive growth of the Internet, consumers and telecommunication companies alike are seeking new methods for high speed data transmission. In particular, telecommunication companies and other entities are developing methods for supporting digital communication circuits at increased speed and/or distances than have existed in the past. For example, new methods for supporting digital communication circuits at increased speed and/or distance include, but are not limited to, DS1/1C/2, ADSL, SDSL, HDSL, and VDSL. In addition, telecommunication companies and other entities are developing these new methods for use over the existing telephone wiring infrastructure, which is generally composed of twisted pair wires bundled as cables strung over relatively long distances.
In general, wire pairs are twisted to minimize the interference of signals from one pair to another caused by radiation or capacitive coupling between the pairs. When a signal is present on a twisted pair, a state known as xe2x80x9cactive,xe2x80x9d the twisted pair naturally creates an electromagnetic field around it. The electromagnetic field thus generated may induce a signal in other twisted pairs located within the electromagnetic field. Additionally, a field generated by one active twisted pair can interfere with the operation of other active pairs located in close proximity to the first pair. As a result, signals transmitted in one pair may generate xe2x80x9cnoisexe2x80x9d within adjoining pairs, thereby degrading or attenuating the signal in the adjoining pairs. This coupling, known as xe2x80x9ccrosstalk,xe2x80x9d worsens as data transmission frequencies and data transmission length increase.
With the emerging deployment of the various high speed digital transport systems and services, the shortcomings of the existing and deployed twisted pair communications cables are quickly being apparent. Emerging methods of supporting digital communication circuits, described above, rely upon using increased data transmission frequencies over long distances. For example, normal voice transmissions transmitted over telephone wires occur in a frequency range from greater than 0 to 4 kHz, while DSL applications typically transmit in a frequency range from greater than 0 to about 100 kHz over distances between 12,000 and 18,000 feet. As can be appreciated, emerging digital communications methods are highly prone to error due to crosstalk between pairs within the cable, between adjoining cables, and from outside interference, especially at the point where the incoming signal is interfaced to transport equipment such as a modem.
Typically, existing twisted pair cables attempt to isolate outside interference and crosstalk by using a common shield within the cable and by grounding the shield at a termination point. Alternatively, if multiple shields are used, existing cables fail to isolate various shields within a cable, such that the multiple shields within a cable electrically communicate with each other, especially after prolonged use. Specifically, if a telecommunications cable includes an overall shield surrounding a unit shield, the overall shield may electrically communicate with the unit shield, or else electrical interaction may occur due to shield shorts for pinholes in any insulation. Moreover, typical telecommunications cables currently in use terminate the overall shield by drawing out a drain wire and simply clamping it to ground. Unfortunately, grounding the drain wire usually causes it to act as an antenna that draws interference into the cable from outside sources.
A cable for supporting digital communication circuits and increased speed and/or distances is disclosed. The cable design employs multiple binder units, each binder unit comprising a predetermined number of twisted pairs. Each binder unit is enclosed by a binder core wrap. The binder core wrap is enclosed by a foil free edge tape applied with the foil facing inwardly and a drain wire pulled between the foil and the core wrap. A preselected number of binder units further comprise a cable. The preselected number of binder units are enclosed by an overall core wrap, and a unit shield is applied over the top of the overall core wrap such that the shield surface faces inwardly for improved termination to ground. An overall drain wire is placed between the overall core wrap and overall shield. Finally, the entire cable may be enclosed by a jacket or sheath.
In the cable of the present invention, the overall shield is isolated from the unit shields, and each shield may be terminated to ground independently of the other. In this way, the inner binder units are isolated from outside interference, e.g., from other adjacent cables. The shields are also isolated from contacting each other or from contacting individual wires or wire pairs, by the overall core wrap, thereby preventing shorts or signal loss through pinholes in the twisted pair insulation.
Moreover, both the overall shield and the unit shield are applied with the foil side inwardly oriented. This arrangement allows the foil to be folded back over the cable and the binder unit, respectively, and terminated using a simple grounding clamp, rather than by grounding the drain wire as is currently the practice. By clamping the shields instead of the drain wire, shielding performance is enhanced because the drain wires are not able to act as an antenna and draw interference into the cable.
By separating the twisted pair wires into manageably sized binder units, convenience and efficiency of use is enhanced. For example, separate digital services may be provided through each of the binder units based upon the frequency spectrum within which they operate. Alternatively, one binder unit may be used as a xe2x80x9csendxe2x80x9d unit, while an adjacent binder unit may be designated the xe2x80x9creceivexe2x80x9d units. By separating xe2x80x9csendxe2x80x9d and xe2x80x9creceivexe2x80x9d functions between binder units, rather than simply between twisted pairs within a single unit, local crosstalk is minimized, leading to increased transmission distances.